commit 307473dec0e2fa966037d04725a40b33669dddc8
author Manman Ren <mren@apple.com> Fri Jun 15 21:32:12 2012 +0000
committer Manman Ren <mren@apple.com> Fri Jun 15 21:32:12 2012 +0000
tree bf59f915327ca87811406874fc88a9a46b692f9e
parent 695fd1a4555aae6cef9292d0d39967a949ea8782

ARM: optimization for sub+abs.

This patch will optimize abs(x-y)
FROM
sub, movs, rsbmi
TO
subs, rsbmi

For abs, we will use cmp instead of movs. This is necessary because we already
have an existing peephole pass which optimizes away cmp following sub.

rdar: 11633193


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158551 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM/ARMISelLowering.cpp

diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index c48fa76..bf17f15 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -6808,9 +6808,6 @@
     MachineRegisterInfo &MRI = Fn->getRegInfo();
     // In Thumb mode S must not be specified if source register is the SP or
     // PC and if destination register is the SP, so restrict register class
-    unsigned NewMovDstReg = MRI.createVirtualRegister(isThumb2 ?
-      (const TargetRegisterClass*)&ARM::rGPRRegClass :
-      (const TargetRegisterClass*)&ARM::GPRRegClass);
     unsigned NewRsbDstReg = MRI.createVirtualRegister(isThumb2 ?
       (const TargetRegisterClass*)&ARM::rGPRRegClass :
       (const TargetRegisterClass*)&ARM::GPRRegClass);
@@ -6827,12 +6824,10 @@
     // fall through to SinkMBB
     RSBBB->addSuccessor(SinkBB);
 
-    // insert a movs at the end of BB
-    BuildMI(BB, dl, TII->get(isThumb2 ? ARM::t2MOVr : ARM::MOVr),
-      NewMovDstReg)
-      .addReg(ABSSrcReg, RegState::Kill)
-      .addImm((unsigned)ARMCC::AL).addReg(0)
-      .addReg(ARM::CPSR, RegState::Define);
+    // insert a cmp at the end of BB
+    AddDefaultPred(BuildMI(BB, dl, 
+                           TII->get(isThumb2 ? ARM::t2CMPri : ARM::CMPri))
+                   .addReg(ABSSrcReg).addImm(0));
 
     // insert a bcc with opposite CC to ARMCC::MI at the end of BB
     BuildMI(BB, dl,
@@ -6844,7 +6839,7 @@
     // by if-conversion pass
     BuildMI(*RSBBB, RSBBB->begin(), dl,
       TII->get(isThumb2 ? ARM::t2RSBri : ARM::RSBri), NewRsbDstReg)
-      .addReg(NewMovDstReg, RegState::Kill)
+      .addReg(ABSSrcReg, RegState::Kill)
       .addImm(0).addImm((unsigned)ARMCC::AL).addReg(0).addReg(0);
 
     // insert PHI in SinkBB,
@@ -6852,7 +6847,7 @@
     BuildMI(*SinkBB, SinkBB->begin(), dl,
       TII->get(ARM::PHI), ABSDstReg)
       .addReg(NewRsbDstReg).addMBB(RSBBB)
-      .addReg(NewMovDstReg).addMBB(BB);
+      .addReg(ABSSrcReg).addMBB(BB);
 
     // remove ABS instruction
     MI->eraseFromParent();